The present invention relates to digital image compositing.
A digital image can include one or more regions. A region of the digital image, as used in this specification, refers to a group of pixels whose association can be arbitrary or otherwise. Pixels can be grouped, for example, such that the region they define represents a real world material such as hair, grass, sky, or wood. A region can represent one or more real world materials and different regions can represent different real world materials. A region can but need not be contiguous and may be made up of two or more non-contiguous parts. A region can include pixels that are associated with other regions.
A region representing a real world material usually does not consist of only one color. Rather, the region typically includes multiple colors, spatially arranged in a manner that represents the appearance of the material. For example, a region that represents grass can include various shades of green and perhaps other colors as well. A region of foliage can include various shades of green and brown. A spatial arrangement of colors over one or more pixels is referred to in this specification as a color arrangement. A color arrangement that can characterize an appearance of a material will be referred to in this specification as visual texture.
In a computer application for editing digital images, for example, Adobe® Photoshop® available from Adobe Systems of San Jose, Calif., it can be quite useful to be able to select a region that corresponds to a single real world material and modify the selected region in isolation of the surrounding pixels or regions. Having this capability, for example, would allow one to change the color only of the hair of a person being portrayed in a digital image, while maintaining the same color or colors of pixels surrounding the hair. The selection and isolation of a region that represents a real world material or object is referred to in this specification as object extraction. Object extraction from a digital image typically includes segmentation of the image into regions, each of which represents a single real world material. Segmentation usually includes locating a boundary between two regions. Segmentation usually includes determining which pixel belongs to which region.